Core component of a liquid crystal optical phased array (LCOPA) device is a liquid crystal grating comprising electrodes arranged in parallel, between which voltages are applied so that an electric field is formed therebetween to control rotation of liquid crystal.
FIG. 1 is a schematic diagram of a structure of a liquid crystal grating in a LCOPA device of the prior art, FIG. 2 is a schematic diagram of isopotential lines of the electric field inside the liquid crystal grating shown in FIG. 1, and FIG. 3 is a graph illustrating phases of incident light controlled by the liquid crystal grating shown in FIG. 1. As shown in FIG. 1, this liquid crystal grating includes: an upper substrate 1 and a lower substrate 4 provided opposite to each other, liquid crystal 8 filled between the upper substrate 1 and the lower substrate 4, a common electrode 2 formed on the upper substrate 1, and a plurality of electrodes 201 formed on the lower substrate 4, and gaps 202 are formed between adjacent electrodes 201. Further, an alignment layer 301 is further formed on the common electrode 2, and an alignment layer 302 is also formed on the electrodes 201. With voltages applied to the plurality of electrodes 201, respectively, electric fields are formed between the electrodes 201 and the common electrode 2, and the liquid crystal 8 is driven to rotate by the electric fields, thus achieving phase control on incident light. FIGS. 2 and 3 are simulation diagrams of electric fields inside the liquid crystal grating shown in FIG. 1 and controlled phases of incident light, and FIGS. 2 and 3 correspond to each other. Here, the electrodes 201 have a width of 3 μm, the gaps 202 have a width of 2 μm, liquid crystal cell has a thickness of 5 μm, and voltages gradually decrease from left end to right end. In FIG. 3, only changes in phases of incident light corresponding to a first 50 μm from left end of the liquid crystal grating are depicted. It should be noted that FIG. 2 is merely a schematic diagram simulating the inner electric field, and the ratio of length to width of the liquid crystal grating in FIG. 2 is not to scale.
As shown in FIG. 2, a sharp drop occurs at positions of the isopotential lines of the electric field inside the liquid crystal grating corresponding to the gaps 202 in the prior art, and also, a distance between two adjacent isopotential lines increases abruptly. As the tangential direction of an isopotential line is always perpendicular to that of an electric field line, density of the isopotential lines reflects electric field intensity, and therefore, directions of the electric fields at the gaps 202 may change abruptly, and intensities of the electric fields at the gaps 202 may also decrease abruptly. Thus, the electric fields inside the liquid crystal grating in the prior art do not change continuously and smoothly.
As shown in FIG. 3, the directions of the electric fields at the gaps 202 may change abruptly, and intensities of the electric fields at the gaps 202 may also decrease abruptly, which causes the phases of incident light at the gaps 202 to increase abruptly, and thus, the phase curve of incident light may bulge at positions corresponding to the gaps, for example, a portion of the phase curve corresponding to abscissa values of 3 μm to 5 μm.
From the above, in the liquid crystal grating of the prior art, the electrodes on the lower substrate are discrete, and as a result, with voltages applied to the electrodes, the electric field at the gaps between respective adjacent electrodes changes abruptly and the electric field inside the liquid crystal grating cannot varies continuously and smoothly, which further leads to that the existing liquid crystal grating fails to control the phases of incident light continuously and smoothly.